The major objective is to study at the genetic, chemical and molecular level the antigen profile of the human lymphoid cell membrane to obtain a better understanding of its role in defense and recognition of disease. Progress towards these objectives included the development of new and effective methods to isolate HLA antigens from serum and urine and to produce monospecific xenoantibodies against these antigens. These reagents proved useful for the isolation and immunochemical characterization of HLA antigens. Somatic cell hybridization was used to demonstrate a linkage between HLA antigens and receptors for complement components C3b and C3d. Man-mouse hybrids were also utilized to demonstrate a linkage between a B-cell receptor and HLA antigens. Efforts were successful to develop new methods for the effective isolation of human B and T lymphocytes rosetting techniques with monkey and sheep red blood cells, respectively. In an effort to determine effects of neoplastic information on HLA antigen expression, we found neither qualitative nor quantitative differences in expression of HLA antigens and Beta 2-microglobulin on cultured melanoma cells when compared to fibroblasts and cultured human lymphoid cells derived from the same patient.